1. Field of the Invention
The present invention relates to automobile internal combustion engines, and in particular to a spherical rotary valve assembly for use in an internal combustion engine.
2. Description of the Related Art
Automobile manufacturers have spent billions of dollars in the past 100 years to develop better performing and more efficient engines at a reasonable cost. There are three major performance parameters in internal combustion engines. They are mechanical efficiency, indicated efficiency and volumetric efficiency. Mechanical efficiency measures frictional loss of the engine. The power loss for driving essential parts of the engine such as camshafts and oil pumps for lubrication are accounted for by friction. Indicated efficiency are thermodynamic losses.
The final parameter is volumetric efficiency. This measures the volume of ambient air drawn in per cylinder relative to the overall cylinder volume. Volumetric efficiency increases by increasing the amount of air taken in and expelled from the combustion cylinder during a piston stroke. This factor is critical to engine performance. When more air is drawn into the combustion cylinder, more fuel can be added for combustion, which increases volumetric efficiency and performance. Also, higher air intake generates more power with less rotation of the engine. Thus, greater air intake wastes less power that would otherwise be expended by burning fuel to rotate the crankshaft.
The vast majority of combustion engines today utilize spring-loaded poppet valves to control the intake of air and expulsion of exhaust gasses to and from the combustion cylinder. However, while widely used, these valves have disadvantages. First, the opening and closing of poppet valves during the intake stroke are not optimized relative to piston movement. This is shown in FIG. 1, which shows a one-half period of piston movement during the intake stroke relative to the poppet valve opening. As can be seen, at the beginning of the piston stroke while the piston is accelerating downward, the amount of air allowed in the by valve is relatively small.
Generally, during the first 20° of downward motion of the piston, the valve is only about 5 to 7% open. This disadvantageously creates a vacuum within the combustion cylinder, which can have significant adverse effects at higher engine RPM. In an optimal interaction, the valve would open up quickly, early in the piston stroke, to allow maximum air intake during the maximum downward acceleration of the piston.
Additionally, the poppet valve moves into and out of the combustion cylinder, generally along the same axis as the piston. If the timing is not controlled properly, it can occasionally happen that the piston hits the poppet valve during its motion, which contact can damage or snap off the poppet valve. Furthermore, poppet valves have a high number of intricate parts. For example, in a 4-cylinder engine with 4 valves per cylinder, the valves would have at minimum 96 parts.
Many of the disadvantages of poppet valves can be overcome by rotary valves. However, owing to problems relating to heat transfer through the valves and air flow into and out of the combustion cylinder through the valves, rotary valves have not been widely accepted. One difficulty with the use of rotary valves is the sealing of the interface between the combustion cylinder and the valve. During the compression stroke and power stroke of the piston, the rotary valve seals the top of the combustion cylinder. Attempts have been made to place a seal at the interface between the combustion cylinder and valve. The seal must be tight to prevent compressed air and gas from escaping the cylinder around the seal during the compression and/or power cycle, which leaking creates efficiency losses as well as emissions. However, as the valve is rotating in contact with the upper edges of the combustion cylinder, the contact between the rotating valve and cylinder seal must be lubricated. It is known to provide a small amount of lubricant to the seal or to provide vapor lubricant into the mixture. However, these methods introduce lubricant into the combustion cylinder, which leads to added emissions and poor combustion quality with detonation. This has been one of the biggest problems in designing rotary valves.
Self-lubricating materials are known, such as for example graphite. However, materials such as graphite generally have a maximum operating temperature in the range of 600° C. before their lubricating qualities break down. Lewis Research Center, Cleveland, Ohio produces a composite coating referred to as PS 300. PS 300 is a composite of metal-bonded chromium oxide with barium fluoride/calcium fluoride eutectic and silver as solid lubricant additives. The maximum operating temperature of this composite is 800° C. before the lubricating ability of the coating breaks down. The problem with the use of such self-lubricating materials as a seal in internal combustion cylinders is that the temperature within the combustion cylinder that would be seen by the seal far exceeds the effective operating temperature of such materials.